Unifying Japan: the Warring States Period

A bird with

One body but

Two beaks,

Pecking itself

To death.

— Anonymous poem from 1500

Intro to the Sengoku Period

Japan was not always a unified nation. At one point in its history, several clans waged war for control of the islands. The Sengoku Period (Warring States Period) was a series of civil wars which took place throughout the 15th and 16th centuries. It finally culminated in the unification of Japan and the establishment of the Tokugawa Shogunate.

Setting the Scene for War

The Sengoku period (1467–1600) coincided with the Muromachi Period (1336–1573) and the rule of the Ashikaga shogunate. During this time, Japan was a feudal society, with the emperor in Kyoto serving as a symbolic figurehead while regional warlords (daimyō) held real political and military power.

The event that triggered the Sengoku period was the Ōnin War (1467–1477), a succession crisis over who would become the next shōgun. The conflict divided powerful clans into two opposing factions, leading to a decade-long war. When the western lords finally withdrew their forces from Kyoto, much of the city lay in ruins, and the Ashikaga shogunate’s authority was severely undermined. Returning to their provinces after the war, many daimyō found that their subordinates had seized power in their absence or declared independence, establishing their provinces as separate domains.

With the collapse of central authority, Japan entered a period of prolonged conflict, with each region vying for power and territory. Military might and strategic alliances became crucial to survival and expansion.

The Role of the Samurai

During the Muromachi Period, Japan was deeply hierarchical. The samurai served as the primary military force for the daimyō, the powerful lords who ruled their respective territories. Samurai were highly skilled warriors, trained in the use of the katana, spears, archery, and later, firearms. They often held high-ranking positions in the daimyō's armies, leading units of ashigaru (足軽, foot soldiers) and devising strategies for warfare.

Iwanari Tomomichi, one of the three great samurai of the Miyoshi clan

Samurai were bound by a code of loyalty to their daimyō, pledging their lives to protect and fight for their lord’s interests. Bushido, the samurai code, emphasised honour, loyalty, and martial skill. Those who failed to uphold these ideals, particularly in cases of disobedience or betrayal, faced severe consequences, including seppuku (ritual suicide) to restore honour. However, during the Sengoku Period, loyalty became more fluid. Samurai often shifted allegiances, driven by changing power dynamics or opportunities for personal advancement.

Samurai were not only warriors but also landholders. In exchange for military service, they were granted fiefs (land holdings) by their daimyō, from which they derived income to support their households. Some samurai also took on administrative roles, managing the lands and villages under their control. They oversaw agriculture, collected taxes, and maintained order in their territories.

Despite the widespread warfare, samurai were also custodians of culture. They were patrons of the arts, particularly those influenced by Zen Buddhism, such as the tea ceremony, calligraphy, and poetry. Samurai also participated in cultural traditions like Noh theatre and contributed to the construction of castles and gardens, many of which became lasting symbols of samurai prestige and influence.

Sengoku period warlord helmets (kabuto)

The Impact of Firearms

Matchlock guns were introduced by the Portuguese in 1543 and quickly became essential for success on the battlefield. The rise of large-scale armies composed of foot soldiers armed with firearms made it increasingly difficult for smaller lords to maintain independence. As a result, these lesser domains were consolidated under powerful Sengoku daimyō (戦国大名, feudal lords of the Sengoku period), who controlled vast territories. The introduction of firearms intensified both the scale and brutality of battles between these warlords. The changing nature of warfare also forced the samurai to adapt, integrating firearms alongside their traditional weapons. While samurai continued to play critical leadership roles, the use of firearms diminished the dominance of mounted samurai in battle.

Ashigaru firing matchlock guns

Oda Nobunaga: The First Great Unifier

One daimyō who fully embraced this new technology was Oda Nobunaga, one of the "great unifiers" of Japan, alongside Toyotomi Hideyoshi and Tokugawa Ieyasu. Nobunaga not only recognised the strategic advantage of firearms but also took steps to secure their production by bringing key gunsmithing centres under his control. He cultivated strong relationships with the Portuguese and the merchants of Sakai, which had become a major international trading port.

As the head of the Oda clan, Nobunaga emerged as the most powerful daimyō in the struggle to unify Japan. In 1573, he overthrew the Ashikaga shogunate and by 1580 had conquered most of Honshū. However, his rise to power was cut short in 1582 when he was betrayed by his vassal Akechi Mitsuhide in the Honnō-ji Incident. Surrounded by enemy forces during a siege on the temple where he was staying, Nobunaga was forced to commit seppuku.

Toyotomi Hideyoshi: From Soldier to Shōgun

Toyotomi Hideyoshi was a retainer of Oda Nobunaga. Coming from a peasant background, Hideyoshi distinguished himself, rising from the rank of foot soldier to samurai, and eventually to Sengoku daimyō. Upon hearing of his master's betrayal and death, he quickly made peace with the Mōri clan, with whom he was at war. He then hurried to Kyoto and avenged Nobunaga only 11 days after his death by defeating Akechi Mitsuhide at the Battle of Yamazaki.

Later in 1582, Hideyoshi defeated Shibata Katsuie and Oda Nobutaka—rivals in the struggle for Nobunaga's succession—at the Battle of Shizugatake. In 1583, he began construction of Osaka Castle, a symbol of his growing power. The following year, Hideyoshi fought fiercely against the allied forces of Tokugawa Ieyasu and Oda Nobuo at the Battle of Komaki and Nagakute, managing to secure a truce. By 1590, Hideyoshi had subdued the regions of Shikoku, Kyūshū, and Kantō. He also forced the clans of the Tōhoku region to swear allegiance to him, finally achieving the unification of Japan.

Throughout his military campaigns and consolidation of power, Hideyoshi valued ability and loyalty over noble birth. He promoted individuals based on merit, allowing people of lower social standing, especially foot soldiers, to rise through the ranks.

After unifying Japan, Toyotomi Hideyoshi turned his ambitions outward, launching invasions of Korea with the ultimate goal of conquering Ming China. Driven by a desire for conquest and prestige, as well as a strategy to secure resources and wealth, Hideyoshi initiated the Imjin War, a campaign that lasted from 1592 to 1598. Despite initial successes, the invasion ultimately failed, and the war ended with Hideyoshi’s death in 1598.

Toyotomi Hideyoshi by unknown artist

Tokugawa Ieyasu: The Final Unifier 

Tokugawa Ieyasu was a close ally of Oda Nobunaga and initially supported Toyotomi Hideyoshi as Nobunaga's successor. However, after Hideyoshi’s death in 1598, a power struggle arose. Hideyoshi's son and heir, Hideyori, was only five years old at the time, and a conflict soon erupted between factions loyal to the Toyotomi clan and those aligned with Ieyasu. This culminated in the Battle of Sekigahara on October 21, 1600, where 160,000 men faced off. Ieyasu’s forces decisively defeated the western army led by Ishida Mitsunari, solidifying his control over Japan. In 1603, Ieyasu was appointed shogun by the emperor, officially marking the beginning of the Tokugawa Shogunate. Under his leadership, he implemented strict policies to control the daimyō, ensuring loyalty and centralising power. His rule marked the beginning of the Edo period, a time of peace, stability, and economic prosperity that lasted for over 250 years.

Edo period screen depicting the Battle of Sekigahara

Cultural Developments Amid Conflict

Despite political instability, the Muromachi period was a time of cultural and economic growth. During the Muromachi period, trade with China under the Ming dynasty flourished. Agricultural productivity improved, leading to population growth and the development of market towns around castles. Zen Buddhism had a profound influence on the arts, including gardens, tea ceremonies, and flower arranging. Two significant temples, the Temple of the Golden Pavilion (金閣寺, kinkaku-ji) and the Serene Temple of the Silver Pavilion (銀閣寺、ginkaku-ji), were also constructed during this time.

Temple of the Golden Pavilion, Kyoto

Bibliography

History of Japan: The Feudal Era to Modern Periods (historycooperative.org)

Sengoku period - Wikipedia

Henshall, 243